Force and Motion

Mousetrap Education Don’t be in the wrong place at the wrong time. Time and chance happen to us all. One thing leads to another. Actions have consequences. Causality –Law of cause and effect –Sewing and reaping (Gal. 6:7-9)

Newton’s 1 st Law An object at rest remains at rest and an object in motion remains in uniform straight line motion unless acted on by an unbalanced force.An object at rest remains at rest and an object in motion remains in uniform straight line motion unless acted on by an unbalanced force. Inertia - Property of matter that resists changes in motion.Inertia - Property of matter that resists changes in motion. Is inertia good or bad?

Newton’s 2nd Law Newton’s 2nd Law - The rate of change in momentum is equal to the net force acting on the body. Ex. What force must be applied to a 40 kg ball for its velocity to be

Additional Info Will use summation notation for net force. Units for force –From dimensional analysis –In metric will use a newton (N) 300 N 450 N 350 N 200 N Which way will the ring move?

Fundamental Forces Gravitational - Masses attract Electrical - Unlike charges attract Magnetic - Unlike poles attract Weak - Responsible for radioactive decay Strong - Holds the nucleus of the atom together

Weight Weight - The force due to gravity. What is the weight of Alexeyev on the moon? On Jupiter? At 157 kg and lifting 246 kg

Newton’s 2 nd Law and Weight Ex. You and your bike weigh 882 N. If your brakes can exert a force of 200 N, what stopping distance do you need if you are traveling at 11 m/s? 

Elevator Ride You stand on a scales while in an elevator. You know you weigh 150 lbs, but the scales say you weigh 180 lbs. What is happening in the elevator? It is stationary. It is moving upward at constant v. It is moving downward at constant v. It is moving upward at increasing v. It is moving downward at increasing v. It is accelerating upward. It is accelerating downward.

Elevator (Cont.) Ex. You stand on a scales while in an elevator. You know you weigh 150 lbs., but the scales say you weigh 180 lbs. What is your acceleration? W FsFs

Newton’s 3 rd Law For every action there is an equal and opposite reaction. F AB F BA

Newton’s 3rd Law m earth = 5.97 × kg Ex. A 110 kg skydiver accelerates towards the earth at 9.8 m/s². How does the earth respond to him?

Hooke’s Law Hooke’s Law - The force exerted by a spring is proportional to the distance the spring is compressed or stretched from its rest state. k - spring constant (N/m) This is a restoring force. It opposes the displacement from its rest state.

Plan of Action 1.Identify objects of interest. 2.Draw free-body diagram 3.Write Newton’s 2nd Law 4.Choose coordinate system. 5.Write out forces in chosen coordinates. 6.Solve equations symbolically. 7.Check the sense of the problem. 8.Insert the values for numerical answers.

Behind the Scenes A 15 kg stage prop is suspended from the ceiling by two ropes which are each run through a pulley and attached to a 20 kg sandbag. What angle does each rope make with respect to the horizontal? (Assume no friction in pulleys and massless ropes.)

Down the Ramp A 1.1 kg block is at the top of a 8.00 m long ramp that is at an angle of 11.8°. If it starts at rest, how long does it take to get to the bottom of the ramp? (Assume the surface is frictionless.) 

“All the towering materialism which dominates the modern mind rests ultimately upon one assumption; a false assumption. It is supposed that if a thing goes on repeating itself it is probably dead; a piece of clockwork. People feel that if the universe was personal it would vary; if the sun were alive it would dance. This is a fallacy even in relation to known fact. For the variation in human affairs is generally brought into them, not by life, but by death; by the dying down or breaking off of their strength or desire. A man varies his movements because of some slight element of failure or fatigue.” G.K. Chesterton (Orthodoxy) Col. 1:16,17